Fix typo found by #3933

Signed-off-by: Michael Woolweaver <m.woolweaver@icloud.com>

advanced/Templates/gravity.db.sql

@@ -73,7 +73,7 @@ CREATE TABLE domainlist_by_group
 CREATE TABLE client
 (
 	id INTEGER PRIMARY KEY AUTOINCREMENT,
-	ip TEXT NOL NULL UNIQUE,
+	ip TEXT NOT NULL UNIQUE,
 	date_added INTEGER NOT NULL DEFAULT (cast(strftime('%s', 'now') as int)),
 	date_modified INTEGER NOT NULL DEFAULT (cast(strftime('%s', 'now') as int)),
 	comment TEXT